sgsn: Auth and Ciph (WIP)

TODO:
  - split this commit into several smaller ones (fixes, integration,
    triplet management, ...)
  - tests

Sponsored-by: On-Waves ehf
sgsn: Refactored and fixed authentication (TODO)

TODO:
  - Merge with previous patch

Sponsored-by: On-Waves ehf
sgsn: Work on 2 phase authorization (WIP)

This implements the MAP way of subscriber validation when the MS
tries an Attach Request:
  1. perform authentication (optionally invoke the sendAuthInfo
  procedure), starts the AuthAndCiph procedure
  2. perform update location
  3. insert subscriber data
  4. finish the update location
  5. Attach Accept / Attach Reject

This is currently accessible via the VTY interface.

TODO:
  - Apply this to (periodic) RA Update Req
  - Delete Subscriber Data
  - Improve on procedure collisions (repeated Attach Req is sometimes
    not handled properly)
  - PDP info
  - Commit cleanup

Sponsored-by: On-Waves ehf